U.S. patent application number 12/528318 was filed with the patent office on 2010-03-04 for method of preparing toner having core-shell structure and toner prepared using the same.
This patent application is currently assigned to SAMSUNG FINE CHEMICALS CO., LTD. Invention is credited to Duck Kyun Ahn, Dae Ii Hwang, Ii Sun Hwang, Jae Kwang Hwang, Dong Won Kim, Keon li Kim, Jun Hee Lee, Jae Bum Park, Woo Young Yang.
Application Number | 20100055599 12/528318 |
Document ID | / |
Family ID | 39665727 |
Filed Date | 2010-03-04 |
United States Patent
Application |
20100055599 |
Kind Code |
A1 |
Yang; Woo Young ; et
al. |
March 4, 2010 |
METHOD OF PREPARING TONER HAVING CORE-SHELL STRUCTURE AND TONER
PREPARED USING THE SAME
Abstract
A method of preparing a toner having a core-shell structure. The
method includes: preparing a mixture by mixing a resin with acid
groups, a coloring agent and at least one additive with an organic
solvent, and neutralizing the acid groups of the resin with a base;
forming a micro-suspension solution by adding the mixture to a
dispersion medium; forming a toner core by removing the organic
solvent from the micro-suspension; and forming a toner complex
having a core-shell structure by seed-polymerizing at least one
monomer on the surface of the toner core. Thus, the toner that can
prevent hot offsets, improve storage stability at a high
temperature and improve charge stability against environment
changes can be prepared with reduced costs according to the
method.
Inventors: |
Yang; Woo Young;
(Daejeon-City, KR) ; Kim; Keon li; (Daejeon-City,
KR) ; Hwang; Dae Ii; (Daejeon-City, KR) ;
Park; Jae Bum; (Daejeon-City, KR) ; Hwang; Ii
Sun; (Daejeon-City, KR) ; Lee; Jun Hee;
(Daejeon-City, KR) ; Hwang; Jae Kwang;
(Daejeon-City, KR) ; Kim; Dong Won; (Daejeon-City,
KR) ; Ahn; Duck Kyun; (Daejeon-City, KR) |
Correspondence
Address: |
Nixon Peabody LLP
P.O. Box 60610
Palo Alto
CA
94306
US
|
Assignee: |
SAMSUNG FINE CHEMICALS CO.,
LTD
ULSAN-CITY
KR
|
Family ID: |
39665727 |
Appl. No.: |
12/528318 |
Filed: |
February 20, 2008 |
PCT Filed: |
February 20, 2008 |
PCT NO: |
PCT/KR08/00979 |
371 Date: |
August 21, 2009 |
Current U.S.
Class: |
430/110.2 ;
430/137.13 |
Current CPC
Class: |
G03G 9/09392 20130101;
G03G 9/09321 20130101; G03G 9/09385 20130101; G03G 9/0804 20130101;
G03G 9/09371 20130101 |
Class at
Publication: |
430/110.2 ;
430/137.13 |
International
Class: |
G03G 9/08 20060101
G03G009/08 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 23, 2007 |
KR |
10-2007-0018502 |
Claims
1. A method of preparing a toner, the method comprising: preparing
a mixture by mixing a resin with acid groups, a coloring agent and
at least one additive with an organic solvent, and neutralizing the
acid groups of the resin with a base; forming a micro-suspension by
adding the mixture to a dispersion medium; forming a toner core by
removing the organic solvent from the micro-suspension; and forming
a toner composite having a core-shell structure by
seed-polymerizing at least one monomer on the surface of the toner
core.
2. The method of claim 1, wherein the resin with acid groups is a
polyester resin having a number average molecular weight of
2,000-10,000, a poly dispersity index (PDI) of 2-15, a THF
insoluble content of 1 wt % or less, and an acid value of 5-100
mgKOH/g.
3. The method of claim 2, wherein an acid value of the polyester
resin is 7-30 mgKOH/g.
4. The method of claim 1, wherein the coloring agent is in the form
of a coloring pigment master batch wherein the amount of the
coloring pigment in the master batch is in the range of 10 to 60
parts by weight based on 100 parts by weight of the master
batch.
5. The method of claim 1, further comprising: aggregating the
seed-polymerized toner composite; melt-adhering the aggregated
toner composite; and forming toner particles by washing and drying
the melt-adhered toner composite, after forming the toner
composite.
6. The method of claim 1, wherein the resin with acid groups
comprises at least one selected from the group consisting of a
carboxyl group, a phosphoric acid group and a sulfonic acid
group.
7. The method of claim 1, wherein the additive comprises a charge
control agent or a releasing agent.
8. The method of claim 1, wherein the dispersion medium comprises a
polar solvent, a surfactant, a thickener, or a mixture thereof.
9. The method of claim 1, wherein the monomer used in the
seed-polymerization comprises at least one selected from the group
consisting of styrene, n-butyl methacrylate, methacrylic acid,
acrylic acid, divinyl benzene and methacrylate.
10. The method of claim 1, wherein a polymerization initiator used
in the seed-polymerization comprises at least one selected from the
group consisting of potassium persulfate, ammonium persulfate,
benzoyl peroxide, lauryl peroxide, sodium persulfate, hydrogen
peroxide, t-butyl hydroperoxide, cumene hydroperoxide, p-methane
peroxysalt and peroxy carbonate.
11. A toner prepared according to the method of claim 1, and having
a volume average particle size of 2.0-10.0 .mu.m, a 80% span value
of 0.9 or less and a shape factor of 0.6-1.0.
12. An electrophotographic image forming device using the toner
according to claim 11.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATION
[0001] This application is a national phase of International
Application No. PCT/KR2008/000979, entitled "METHOD OF PREPARING
TONER HAVING CORE-SHELL STRUCTURE AND TONER PREPARED USING THE
SAME", which was filed on Feb. 20, 2008, and which claims priority
of Korean Patent Application No. 10-2007-0018502, filed on Feb. 23,
2007 in the Korean Intellectual Property Office, the disclosure of
which is incorporated herein in its entirety by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] The present invention relates to a method of preparing a
toner having a core-shell structure and a toner prepared using the
same, and more particularly, to a method of preparing a toner
having a core-shell structure that reduces manufacturing costs,
prevents hot offset, and improves storage stability at a high
temperature and charge stability against environment changes, and a
toner prepared using the method.
[0004] 2. Background Art
[0005] Recently, a need for toner suitable for a high-speed
printing, particularly toner capable of improving image quality and
preventing hot offset increases in the printing industry. The "hot
offset" is a phenomenon in which some of melted toner on a printing
paper adheres to a fixing device after passing through the fixing
device since too much toner exceeding the amount required to be
fixed on the printing paper is excessively melted when the toner is
heated while passing through the fixing device.
[0006] Generally, a toner is prepared by adding a coloring agent, a
charge control agent, a dye, a pigment, a releasing agent, or the
like to a thermoplastic resin acting as a binder resin. In
addition, inorganic metal fine particles such as silica or a
titanium oxide may be added to toner as external additives in order
to provide toner with fluidity or improve physical properties such
as charge controlling properties or cleaning properties.
[0007] Generally, a polyester resin and a styrene-acrylic resin are
used as a binder resin. Upon comparing those two resins, the
polyester resin has better anti-hot offset properties and color
forming/development properties but poorer stability of charged
amount according to environment changes compared to the
styrene-acrylic resin. Meanwhile, the styrene-acrylic resin has
lower hygroscopic properties and better storage stability at a high
temperature than the polyester resin.
[0008] As described above, a toner needs to have anti-hot offset
properties and storage stability, which are contrary to each other,
at a high temperature.
[0009] U.S. Pat. No. 5,604,076 discloses a toner having a
toner-shell structure that can have anti-hot offset properties and
storage stability at a high temperature. A resin dispersion is
prepared by dispersing a polyester resin in an anionic surfactant.
A styrene monomer, an acrylic monomer and a polymerization
initiator are added to the resin dispersion and seed-polymerization
is performed to form a micro-suspension of toner particles having a
polyester resin core/styrene-acrylic resin shell structure. Then, a
separate pigment water-dispersion is added to the micro-suspension
and the mixture is aggregated to prepare a toner having a
core-shell structure. Here, the pigment water-dispersion is
prepared by dispersing a pigment in a cathionic surfactant.
However, since the pigment is inevitably exposed on the surface of
the toner according to the method by adding the separate pigment
dispersion to the micro-suspension and aggregating the mixture,
charge properties may be deteriorated. Furthermore, the
manufacturing process may become complex since the resin dispersion
and pigment dispersion are respectively prepared for the
preparation of the toner particles.
DISCLOSURE OF THE INVENTION
[0010] The present invention provides a method of preparing a toner
with reduced costs and a toner prepared using the method.
[0011] The present invention also provides a method of preparing a
toner that can prevent hot offsets and a toner prepared using the
method.
[0012] The present invention also provides a method of preparing a
toner that can improve storage stability at a high temperature and
a toner prepared using the method.
[0013] The present invention also provides a method of preparing a
toner that can improve charge stability against environment changes
and a toner prepared using the method.
[0014] The present invention also provides an electrophotographic
image forming device using the toner.
[0015] According to an aspect of the present invention, there is
provided a method of preparing a toner, the method comprising:
[0016] preparing a mixture by mixing a resin with acid groups, a
coloring agent and at least one additive with an organic solvent,
and neutralizing the acid groups of the resin with a base; [0017]
forming a micro-suspension by adding the mixture to a dispersion
medium; [0018] forming a toner core by removing the organic solvent
from the micro-suspension; and [0019] forming a toner composite by
adding at least one monomer and a polymerization initiator to the
toner core and seed-polymerizing the resultant using the toner core
as a polymerization seed.
[0020] The resin with acid groups may be a polyester resin having a
number average molecular weight of 2,000-10,000, a poly dispersity
index (PDI) of 2-15, a THF insoluble content of 1 wt % or less, an
acid value of 5-100 mg KOH/g.
[0021] An acid value of the polyester resin may be 7-30
mgKOH/g.
[0022] The coloring agent may be in the form of a coloring pigment
master batch wherein the amount of the coloring pigment in the
master batch is in the range of 10 to 60 parts by weight based on
100 parts by weight of the master batch.
[0023] The method may further comprise: aggregating the
seed-polymerized toner composite; melt-adhering the aggregated
toner composite; and forming toner particles by washing and drying
the melt-adhered toner composite, after forming the toner
composite.
[0024] The resin with acid groups may comprise at least one acid
group selected from the group consisting of a carboxyl group, a
phosphoric acid group and a sulfonic acid group.
[0025] The additive may comprise a charge control agent or a
releasing agent.
[0026] The dispersion medium may comprise a polar solvent, a
surfactant, a thickener, or a mixture thereof.
[0027] The monomer used in the seed-polymerization may comprise at
least one selected from the group consisting of styrene, n-butyl
methacrylate, methacrylic acid, acrylic acid, divinyl benzene and
methacrylate.
[0028] A polymerization initiator used in the seed-polymerization
may comprise at least one selected from the group consisting of
potassium persulfate, ammonium persulfate, benzoyl peroxide, lauryl
peroxide, sodium persulfate, hydrogen peroxide, t-butyl
hydroperoxide, cumene hydroperoxide, p-methane peroxy salt and
peroxy carbonate.
[0029] According to another aspect of the present invention, there
is provided a toner prepared according to the method and having a
volume average particle size of 2.0-10.0 .mu.m, a 80% span value of
0.9 or less and a shape factor of 0.6-1.0.
[0030] According to another aspect of the present invention, there
is provided an electrophotographic image forming device using the
toner.
BEST MODE FOR CARRYING OUT THE INVENTION
[0031] Hereinafter, the present invention will now be described
more specifically with reference to exemplary embodiments of the
invention.
[0032] Toner particles prepared according to a method of an
embodiment of the present invention include a toner core and a
shell.
[0033] The toner core which includes a resin with acid groups, a
coloring agent and at least one additive is prepared in the form of
being dispersed in a dispersion medium, and the shell is formed by
adding at least one monomer and a polymerization initiator to the
toner core dispersed in the dispersion medium and seed-polymerizing
the resultant using the toner core as a polymerization seed. [0034]
First, a resin with acid groups is described.
[0035] The acid groups are introduced to the resin by chemical
bonding. Such acid group which can be neutralized by a base becomes
an anion in an aqueous solution and gives hydrophilic properties.
Accordingly, the resin with acid groups can be dispersed and
stabilized in the particulate form within an aqueous solution. The
acid group may be at least one selected from the group consisting
of a carboxyl group, a phosphoric acid group and a sulfonic acid
group.
[0036] The resin with acid groups may include a polyester resin
which is suitable for dispersion of a coloring agent and has good
fixing properties(fixability) at a low temperature. The polyester
resin may be prepared by including a monomer compound having an
acid group which can be neutralized as an essential ingredient, and
examples of the polyester resin are a carboxyl group-containing
polyester resin, a sulfonic acid group(such as dimethyl
5-sulfoisophthalate sodium salt)-containing polyester resin, or a
phosphoric acid-containing polyester resin. Among these, the
carboxyl group-containing polyester-based resin is preferable, in
which a number average molecular weight may be 2,000-10,000, a poly
dispersity index (PDI) may be 2-15, a THF insoluble content may be
1 wt % or less, a glass transition temperature may be 45-75.degree.
C., a softening temperature (Ts) may be 130-190, and an acid value
may be 5-100 mg KOH/g. When the number average molecular weight is
less than 2,000, the melt viscosity becomes too low and the range
of fixing temperature becomes narrow. On the other hand, when the
number average molecular weight is greater than 10,000, large
particles are formed while forming particles, and particle size
distribution is widened. Furthermore, when the PDI is less than 2,
the range of fixing temperature becomes narrow. On the other hand,
when the PDI is greater than 15, it becomes difficult to obtain a
resin having THF insoluble content of less than 1 wt %. When the
THF insoluble content is greater than 1 wt %, it is difficult to
prepare micro-suspended particles. Moreover, when the acid value is
lower than 5 mg KOH/g, the toner micro-suspension which will be
described later may not be easily prepared. On the other hand, when
the acid value is greater than 100 mg KOH/g, environmental
stability of the prepared toner may be significantly decreased.
More preferably, the acid value is 7-30 mg KOH/g.
[0037] Here, the polyester resin may be prepared by
condensation-polymerization in which polyhydric alcohol components
and polybasic carboxylic acid components are mixed and heated,
optionally, under reduced pressure and/or in the presence of a
catalyst. Examples of the polyhydric alcohol components are
polyoxyethylene-(2.0)-2,2-bis(4-hydroxyphenyl)propane,
polyoxypropylene-(2.0)-2,2-bis(4-hydroxyphenyl)propane,
polyoxypropylene-(2.2)-polyoxyethylene-(2.0)-2,2-bis(4-hydroxyphenyl)prop-
ane, polyoxyethylene-(2.3)-2,2-bis(4-hydroxyphenyl)propane,
polyoxypropylene-(6)-2,2-bis(4-hydroxyphenyl)propane,
polyoxypropylene-(2.3)-2,2-bis(4-hydroxyphenyl)propane,
polyoxypropylene-(2.4)-2,2-bis(4-hydroxyphenyl)propane,
polyoxypropylene-(3.3)-2,2-bis(4-hydroxyphenyl)propane,
polyoxyethylene-(6)-2,2-bis(4-hydroxyphenyl)propane, ethylene
glycol, 1,3-propylene glycol, 1,2-propylene glycol, 1,4-butylene
glycol, 1,3-butylene glycol, and glycerol. Examples of the
polybasic carboxylic acid components are an aromatic or aliphatic
polybasic acid and/or an alkyl ester thereof those are commonly
used in the preparation of the polyester resin. Examples of the
polybasic acid are terephthalic acid, isophthalic acid, trimellitic
acid, pyromellitic acid, 1,2,4-cyclohexane tricarboxylic acid,
2,5,7-naphthalene tricarboxylic acid, 1,2,4-naphthalene
tricarboxylic acid, 1,2,5-hexane tricarboxylic acid, 1,2,7,8-octane
tetracarboxylic acid, and/or alkyl esters of these carboxylic
acids, wherein the alkyl group may be a methyl group, an ethyl
group, a propyl group and a butyl group. The polybasic acid and/or
alkyl esters thereof may be used alone or in a combination of at
least two of them.
[0038] The content of the resin with acid groups may be in the
range of 50 to 98 parts by weight based on 100 parts by weight of
the total toner core. When the content is less than 50 parts by
weight, the resin is insufficient for binding the components of the
toner core. On the other hand, when the content is higher than 98
parts by weight, the amount of the toner core except for the resin
is too small to preserve the function of the toner. Here, the toner
core includes a coloring agent and an additive which will be
described later in addition to the resin with acid groups.
[0039] Meanwhile, the coloring agent is not used in the form of the
coloring pigment itself, but in the form of a coloring pigment
master match in which the coloring pigment is dispersed in a resin.
The coloring pigment master batch indicates a resin composition in
which a coloring pigment is uniformly dispersed. The coloring
pigment master batch is prepared by blending a coloring pigment and
a resin at a high temperature and high pressure, or by adding a
coloring pigment to a resin solution and applying a high shearing
force to disperse the coloring pigment. By using the coloring
pigment master batch, a uniform micro-suspension can be prepared by
suppressing the exposure of a pigment in the preparation of toner
micro-suspension. In the coloring pigment master batch used in an
embodiment of the present invention, the amount of the coloring
pigment may be in the range of 10-60 parts by weight, preferably
20-40 parts by weight based on 100 parts by weight of the coloring
pigment master batch. When the amount of the coloring pigment is
less than 10 parts by weight, a desired color may not be reproduced
due to too low amount of the pigment of the toner. On the other
hand, when the pigment is greater than 60 parts by weight, the
pigment dispersion may not be uniform within the coloring pigment
master batch.
[0040] The coloring pigment may be selected appropriately from
pigments commonly and commercially used such as a black pigment, a
cyan pigment, a magenta pigment, a yellow pigment and a mixture
thereof.
[0041] Examples of the pigments are as follows. That is, a titanium
oxide or carbon black may be used as the black pigment. A copper
phthalocyanine compound and derivatives thereof, an anthraquine
compound or a base dye lake compound can be used for the cyan
pigment. In particular, a C.I. pigment blue 1, 7, 15, 15:1, 15:2,
15:3, 15:4, 60, 62, 66, or the like can be used. A condensation
nitrogen compound, an anthraquine, a quinacridone compound, a base
dye lake compound, a naphthol compound, a benzo imidazole compound,
a thioindigo compound, or a perylene compound can be used for the
magenta pigment. Particularly, C.I. pigment red 2, 3, 5, 6, 7, 23,
48:2, 48:3, 48:4, 57:1, 81:1, 144, 146, 166, 169, 177, 184, 185,
202, 206, 220, 221, 254, or the like can be used. A condensation
nitrogen compound, an isoindolinone compound, an anthraquine
compound, an azo metal complex, or an allyl imide compound can be
used for the yellow pigment. Particularly, C.I. pigment yellow 12,
13, 14, 17, 62, 74, 83, 93, 94, 95, 109, 110, 111, 128, 129, 147,
168, or the like can be used.
[0042] The amount of the coloring agent may be an amount sufficient
to color the toner and form a visible image by development, and
preferably in the range of 3 to 15 parts by weight based on 100
parts by weight of the resin with acid groups. When the amount of
the coloring agent is less than 3 parts by weight, coloring effect
is not sufficient. On the other hand, when the amount of the
coloring agent is greater than 15 parts by weight, sufficient
frictional charge amount cannot be obtained due to low electrical
resistance, thereby causing contamination.
[0043] Meanwhile, the additive includes a charge control agent, a
releasing agent or a mixture thereof. [00371 The charge control
agent may be a negative-charging charge control agent and a
positive-charging charge control agent. Examples of the
negative-charging charge control agent are an organic metal complex
or a chelate compound such as azo complex containing a chromium or
a mono azo metal complex; a salicylic acid compound containing
metal such as chromium, iron and zinc; and an organic metal complex
of an aromatic hydroxycarboxylic acid and an aromatic dicarboxylic
acid, and any known negative-charging charge control agent may be
used without limitation. Examples of the positive-charging charge
control agent are Nigrosine and modified products of Nigrosine
modified with a fatty acid metal salt; and an onium salt including
a quaternary ammonium salt such as tributylbenzylammonium
1-hydroxy-4-naphthosulfonate and tetrabutylammonium
tetrafluoroborate. These positive/negative-charging charge control
agents may be used alone or in combination of at least two. Since
the charge control agent stably and quickly charge toner by its
electrostatic force, the toner can be stably supported on a
developing roller.
[0044] The amount of the charge control agent included in the toner
may generally be in the range of 0.1 to 10 parts by weight based on
100 parts by weight of the toner core. When the amount of the
charge control agent is less than 0.1 parts by weight, toner charge
speed is too low and the amount of charging is too low to function
as a charge control agent. On the other hand, when the amount of
the charge control agent is greater than 10 parts by weight, an
overcharge may distort images.
[0045] The releasing agent may enhance the fixing properties of the
toner image, and examples of the releasing agent are polyalkylene
wax such as low molecular weight polypropylene and low molecular
weight polyethylene, ester wax, carnauba wax and paraffin wax. The
amount of the releasing agent included in the toner may be in the
range of 0.1 to 30 parts by weight based on 100 parts by weight of
the toner core. When the amount of the releasing agent is less than
0.1 parts by weight, oilless fixing of toner particles in which
toner particles are fixed without using oil cannot be achieved. On
the other hand, when the amount of the releasing agent is greater
than 30 parts by weight, toner may be flocculated while it is
stored.
[0046] In addition, the additive may further include a long chain
fatty acid, or the like. The long chain fatty acid may be
appropriately used in order to prevent deterioration of developing
properties and obtain high quality images.
[0047] The additive may further include external additives. The
external additive may be used to improve fluidity of toner or
control charge properties, and examples of the external additive
are large particulate silica, small particulate silica and polymer
beads.
[0048] The monomer for polymerization forms a shell surrounding the
toner core including the resin with acid groups, the coloring agent
and the additives. The monomer is added to the toner core with a
polymerization initiator and seed-polymerized to form a shell.
Examples of the monomer are styrene, n-butyl methacrylate,
methacrylic acid, acrylic acid, divinyl benzene, methacrylate and a
mixture thereof. The amount of the monomer in the toner may be in
the range of 10 to 200 parts by weight based on 100 parts by weight
of the toner core. When the amount of the monomer is less than 10
parts by weight, the entire surface of the toner core cannot be
coated by the monomer, and thus storage properties at a high
temperature may be not obtained. On the other hand, when the amount
of the monomer is greater than 200 parts by weight, the releasing
agent, or the like cannot be easily leak out from the toner core
during the fixing since the shell is too thick, thereby decreasing
fixing properties.
[0049] In addition, the polymerization initiator may be potassium
persulfate, ammonium persulfate, benzoyl peroxide, lauryl peroxide,
sodium persulfate, hydrogen peroxide, t-butyl hydroperoxide, cumene
hydroperoxide, p-methane peroxy salt, peroxy carbonate, and a
mixture thereof. The amount of the polymerization initiator may be
in the range of 0.1 to 5 parts by weight based on 100 parts by
weight of the monomer. When the amount of the polymerization
initiator is less than 0.1 parts by weight, polymerization may not
be properly performed. On the other hand, when the amount of the
polymerization initiator is greater than 5 parts by weight,
polymerization may not be easily controlled due to rapid
reaction.
[0050] Hereinafter, a method of preparing a toner according to an
embodiment of the present invention will be described.
[0051] First, a resin with acid groups, a coloring pigment master
batch and at least one additive are mixed with an organic solvent
at a temperature of 40 to 95. Then, the acid group is neutralized
with a base to prepare a mixture.
[0052] Then, the mixture is added to a dispersion medium including
a polar solvent, a surfactant and optionally a thickener at 60-98
and stirred to form a micro-suspension.
[0053] Then, the micro-suspension is stirred at 60-98, and the
organic solvent is removed by evaporation to form a toner core
which is dispersed in the dispersion medium.
[0054] Then, at least one monomer and a polymerization initiator
are added to the toner core and the resultant is seed-polymerized
using the toner core as a polymerization seed. A styrene-acrylic
resin shell surrounding the toner core formed of polyester resin is
formed by the seed-polymerization.
[0055] Then, an aggregating agent is added to the formed toner
composite and the temperature, pH, and the like are controlled to
aggregate the resultant. Here, the aggregated toner composite has a
low rigidity and the shape thereof is very irregular.
[0056] Then, the aggregated toner composite is melt-adhered to
obtain a toner composite having a desired particle size. By such a
melt-adhesion, the rigidity of the toner composite is strengthened,
and the shape becomes regular. In addition, the shape of the toner
composite may change in various shapes from contorted sphere to
complete sphere according to the degree of the melt-adhesion.
[0057] Finally, the melt-adhered toner composite is cooled, washed
and dried to obtain toner particles.
[0058] The organic solvent used in the preparation is volatile, has
a lower boiling point than polar solvents, and does not mix with
polar solvents, and may include at least one type selected from the
group consisting of esters such as methyl acetate or ethyl acetate;
ketones such as acetone or methylethyl ketone; hydrocarbons such as
dichloromethane or tricholoroethane; and an aromatic hydrocarbons
such as benzene.
[0059] The polar solvent may be at least one selected from the
group consisting of water, glycerol, ethanol, ethylene glycol,
propylene glycol, diethylene glycol and dipropylene glycol,
sorbitol, and preferably water.
[0060] The thickener may be polyvinyl pyrrolidone, polyvinyl
alcohol, polyacrylic acid, gelatin, chitosan and sodium
alginate.
[0061] The surfactant may include at least one selected from the
group consisting of a nonionic surfactant, an anionic surfactant, a
cationic surfactant and an amphoteric surfactant.
[0062] Examples of the nonionic surfactant are polyvinyl alcohol,
polyacrylic acid, methycellulose, ethylcellulose, propylcellulose,
hydroxylethylcellulose, carboxymethylcellulose, polyoxyethylene
cetyl ether, polyoxyethylene lauryl ether, polyoxyethylene
octylphenyl ether, polyoxyethylene octylphenyl ether,
polyoxyethylene stearyl ether, polyoxyethylene norylphenyl ether,
ethoxylate, phosphate norylphenols, triton, and
dialkylphenoxypoly(ethyleneoxy)ethanol. Examples of the anionic
surfactant are sodium dodecyl sulfate, sodium dodecyl benezene
sulfonate, sodium dodecyl naphthalene sulfate, dialkyl benzenealkyl
sulfate, and sulfonate. Examples of the cationic surfactant are
alkyl benzene dimethyl ammonium chloride, alkyl trimethyl ammonium
chloride, and distearyl ammonium chloride. Examples of the
amphoteric surfactant are amino acid amphoteric surfactant, betaine
amphoteric surfactant, lecitin, taurin, cocoamidopropylbetaine, and
disodium cocoamphodiacetate. The surfactants described above may be
used alone or in combination of at least two.
[0063] The base used to neutralize the acid groups, that is, a
neutralizer, may be, for example, an alkaline compound such as
sodium hydroxide and lithium hydroxide; a carbonate of an alkaline
metal such as sodium, potassium and lithium; an alkaline metal
acetate; and an alkanolamine such as ammonium hydroxide,
methylamine and dimethylamine, and preferably an alkaline
compound.
[0064] The neutralizer may be used at 0.1-3.0 equivalents,
preferably 0.5-2.0 equivalents, per 1 equivalent of the acid group
of the resin with acid groups.
[0065] The aggregating agent of the toner core may be a surfactant
used in a dispersion, a surfactant having an opposite polarity to
the surfactant used in a dispersion or a monovalent or higher
inorganic metal salt.
[0066] Generally, since the aggregating ability increases as the
ionic charge number increases, an appropriate aggregating agent
needs to be selected in consideration of the aggregating rate of
the dispersion or the stability of the method of preparation.
Examples of the monovalent or higher inorganic metal salt are
calcium chloride, calcium acetate, barium chloride, magnesium
chloride, sodium chloride, sodium sulfate, ammonium sulfate,
magnesium sulfate, sodium phosphate, sodium dihydrophosphate,
ammonium chloride, cobalt chloride, strontium chloride, cesium
chloride, nickel chloride, rubidium chloride, potassium chloride,
sodium acetate, ammonium acetate, potassium acetate, sodium
benzoate, aluminum chloride and zinc chloride.
[0067] The toner prepared by a method according to an embodiment of
the present invention may be applied to an electrophotographic
image forming device. Here, the electrophotographic image forming
device may be a laser printer, a photocopier or a facsimile.
[0068] The present invention will be described in further detail
with reference to the following examples. These examples are for
illustrative purposes only and are not intended to limit the scope
of the present invention.
Examples
[0069] Synthesis of Polyester Resin
Preparation Example 1
Synthesis of Polyester Resin 1
[0070] A 3 L reactor equipped with a stirrer, a nitrogen gas inlet,
a thermometer and a cooler was installed in an oil bath in which
the oil is a heat transfer medium. A variety of monomer, that is 50
parts by weight of dimethyl terephthalate, 47 parts by weight of
dimethyl isophthalate, 80 parts by weight of 1,2-propylene glycol
and 3 parts by weight of trimellitic acid were added to the
reactor. Then, dibutyl tin oxide was added thereto as a catalyst at
a ratio of 500 ppm with respect to the total weight of the
monomers. Then, the reaction temperature was increased to 150 while
stirring the mixture at a speed of 150 rpm. The reaction was
performed for about 6 hours, and then, the reaction temperature was
increased to 220. The pressure of the reactor was reduced to 0. 1
torr in order to remove the byproducts, and the reaction was
completed after maintaining at the pressure for 15 hours. As a
result, polyester resin 1 was obtained.
[0071] The glass transition temperature (Tg) of the polyester resin
1 measured using a differential scanning calorimeter (DSC) was 62.
In addition, the softening temperature (Ts) of the polyester resin
1 measured using a flow tester CFT-500 was 156. The number average
molecular weight and poly dispersity index (PDI) of the polyester
resin 1 were measured by a gel permeation chromatography (GPC)
using polystyrene as a standard sample and they were respectively
4,300 and 3.5. An acid value measured by titration was 15 mg
KOH/g.
Preparation Example 2
Synthesis of Polyester Resin 2
[0072] Polyester resin 2 was prepared in the same manner as in
Preparation Example 1, except that the process of removing
byproducts was performed for 10 hours. As a result of measuring Tg
of the polyester resin 2 using a DSC after the reaction, the Tg was
66. The Ts of the polyester resin 2 measured using a flow tester
CFT-500 was 138. The number average molecular weight and PDI of the
polyester resin 2 which were measured by a GPC using polystyrene as
a standard sample were respectively 2,100 and 3.4. An acid value
measured by titration was 14 mg KOH/g.
[0073] Preparation of Coloring Pigment Master Batch
Preparation Example 3
Preparation of Black Pigment Master Batch
[0074] The polyester resin synthesized in Preparation Example 1 and
a carbon black pigment (Degussa GmbH of Germany, NIPEX 150) were
mixed at a weight ratio of 8:2. Then, 50 parts by weight of ethyl
acetate was added to 100 parts by weight of the polyester resin and
the mixture was heated to about 60, and then stirred with a mixer.
Then, while the mixture was mixed at a rate of 50 rpm using a
biaxial extruder having a vacuum device, ethyl acetate as a solvent
was removed using the vacuum device to obtain a black pigment
master batch.
[0075] Preparation of Toner Particles
Example 1
[0076] 60 g of polyester resin synthesized in Preparation Example
1, 40 g of black pigment master batch synthesized in Preparation
Example 3, 1 g of a charge control agent (N-23;HB Dinglong Co.), 4
g of paraffin wax, and 150 g of methylethyl ketone as an organic
solvent were added to a 1 L reactor equipped with a cooler, a
thermometer, and an impeller stirrer. While the mixture was stirred
at a rate of 600 rpm, 25 ml of 1N NaOH solution was added thereto.
Then, the mixture was mixed at 80 for 5 hours while refluxing. When
the mixture has sufficient fluidity, it was further stirred at 500
rpm for 2 hours. As a result, a toner mixture was obtained.
[0077] 600 g of distilled water, 5 g of a neutral surfactant (Tween
20, Aldrich Co.), and 1 g of sodium dodecyl sulfate (Aldrich Co.)
as an anionic surfactant were added to a separate 3 L reactor
equipped with a cooler, a thermometer and an impeller stirrer, and
the mixture was stirred at 85 at 600 rpm for 1 hour to obtain a
dispersion medium.
[0078] The toner mixture was added to the dispersion medium and
stirred at the same temperature, i.e., 85, at 1000 rpm for 1 hour
to prepare a toner micro-suspension.
[0079] Then, 145 g of methylethyl ketone as an organic solvent was
removed in a partially reduced pressure of 100 mmHg while the
reactor was heated to 90. Thus, a toner core dispersed in the
dispersion medium was obtained. The size of the toner core in which
methylethyl ketone was removed was measured using a Coulter
Multisizer (Beckman Coulter Co.), and the volume average particle
size was 400 nm.
[0080] Then, the temperature in the reactor was cooled to 80, and
30 g of styrene monomer, 4 g of n-butyl methacrylate and 2 g of
methacrylic acid as monomers for polymerization were gradually
added to the reactor for 20 minutes. 0.2 g of potassium persurfate
dissolved in 100 ml of distilled water as a polymerization
initiator was added thereto for 1 hour while the mixture was
stirred at 1000 rpm, and the reactor was further stirred at 80 for
4 hours. As a result, a toner composite having a core-shell
structure was obtained. The size of the toner composite was
measured using a Coulter Multisizer (Beckman Coulter Co.), and the
volume average particle size was 450 nm.
[0081] Subsequently, 10 g of magnesium chloride dissolved in 50 g
of distilled water was gradually added to the reactor, and the
reactor was heated to 80 for 30 minutes to aggregate the toner
composite. After 5 hours, the size of the aggregated toner
composite was measured using a Coulter Multisizer (Beckman Coulter
Co.), and the volume average particle size was 6.7 .mu.m.
[0082] Then, melt-adhesion was performed at 80 for 8 hours by
adding 500 g of distilled water to the reactor, and the reactor was
cooled.
[0083] Then, the melt-adhered toner composite, i.e., toner
particles, were separated using a filter that is commonly used in
the art, washed with 1 N hydrochloric acid solution, and washed
again 5 times with distilled water to completely remove a
surfactant, and the like. The washed toner particles were dried in
a fluidized bed dryer at 40 for 5 hours to obtain dried toner
particles.
[0084] As a result of analyzing the toner particles, the obtained
toner particles had a volume average particle size of 6.8 .mu.m and
a 80% span value of 0.65. In addition, as a result of analyzing 100
random toner particle samples by Image J software using a scanning
electron microscope (SEM; JEOL Ltd.), a mean shape factor was
0.69.
Example 2
[0085] Toner particles were prepared in the same manner as in
Example 1, except that polyester resin 2 synthesized in Preparation
Example 2 was used.
[0086] As a result of analyzing the toner particles, the obtained
toner particles had a volume average particle size of 6.5 .mu.m and
a 80% span value of 0.69. In addition, as a result of analyzing 100
random toner particle samples by Image J software using a scanning
electron microscope (SEM; JEOL Ltd.), a mean shape factor was
0.71.
Comparative Example 1
[0087] Toner particles were prepared in the same manner as in
Example 1, except that seed-polymerization is omitted after forming
the toner micro-suspension.
[0088] As a result of analyzing the toner particles, the obtained
toner particles had a volume average particle size of 6.5 .mu.m and
a 80% span value of 0.65. In addition, as a result of analyzing 100
random toner particle samples by Image J software using a scanning
electron microscope (SEM; JEOL Ltd.), a mean shape factor was
0.65.
Comparative Example 2
[0089] Toner particles were prepared in the same manner as in
Example 1, except that polyester resin 2 synthesized in Preparation
Example 2 was used and seed-polymerization is omitted after forming
the toner micro-suspension.
[0090] As a result of analyzing the toner particles, the obtained
toner particles had a volume average particle size of 6.3 .mu.m and
a 80% span value of 0.68. In addition, as a result of analyzing 100
random toner particle samples by Image J software using a scanning
electron microscope (SEM; JEOL Ltd.), a mean shape factor was
0.69.
[0091] Volume average particles sizes of the toner according to
Examples 1 and 2 and Comparative Examples 1 and 2 were measured
using a Coulter Multisizer 3. An aperture of 100 .mu.m was used in
the Coulter Multisizer, an appropriate amount of a surfactant was
added to 50 to 100 ml of ISOTON-II(Beckman Coulter Co.) as an
electrolyte, and 10 to 20 mg of a sample to be measured was added
thereto, and the resultant was dispersed in a ultrasonic dispersing
apparatus for 1 minute to prepare a sample for the Coulter
Multisizer.
[0092] In addition, the 80% span value which is an index that
determines the particle size distribution was calculated by
Equation 1 below. The volume of toner particles is accumulated from
particles of the smallest size in ascending order until the
accumulated volume reaches 10% of the total volume of the toner. An
average particle size of the accumulated particles is defined as
d10. Average particle sizes of the accumulated particles
corresponding to 50% and 90% of the total volume of the toner are
respectively defined as d50 and d90.
80% span value=(d90-d10)/d50 Equation 1
[0093] Here, a smaller span value indicates a narrow particle
distribution, and a larger span value indicates a wide particle
distribution.
[0094] In addition, the shape factor was calculated by Equation 2
below by measuring SEM images (.times.1,500) of 100 random toner
particles and analyzing them using Image J software.
Shape factor=4.pi.(area/perimeter 2) Equation 2
[0095] Here, the area indicates an projected area of the toner and
the perimeter indicates a projected circumference of the toner. The
shape factor may be in the range of 0 to 1, the closer the value is
to 1, the more spheric the shape is.
[0096] Meanwhile, a method of evaluating resins is as follows.
[0097] Using a differential scanning calorimeter (Netzsch Co.), the
temperature of a sample was increased from 20 to 200 at 10/min,
rapidly cooled to 10 at 20/min, and heated at 10/min to measure a
glass transition temperature (Tg). The median of each tangent with
a baseline near the endothermic curve obtained was defined as
Tg.
[0098] A softening temperature (Ts) was measured using a flow
tester CFT-500 (Shimadzu Co.), and a temperature at which a half of
1.5 g of a sample flow out through a nozzle having a diameter of
1.0 mm and a length of 10 mm in a 10 Kgf load at 6/min was defined
as Ts.
[0099] The acid value (mg KOH/g) was measured by dissolving the
resin in a dichloromethane, cooling the solution and titrating the
solution with 0.1N KOH methyl alcohol solution.
[0100] According to the method, the toner particles are prepared by
including all of the toner components in the preparation of the
micro-suspension, and thus additional process for preparing a
dispersion may be omitted. In addition, charge properties of the
toner may be improved by suppressing exposure of the coloring agent
on the surface of the toner particles using the coloring pigment
master batch.
[0101] Toner particles prepared according to Examples 1 and 2 and
Comparative Examples 1 and 2 were evaluated as follows.
[0102] Storage Stability at a High Temperature
[0103] 10 g of toner, 0.2 g of silica (TG 810G, Cabot co.) and 0.05
g of silica (RX50, Degussa GmbH) were mixed to prepare 10.25 g of a
toner with external additives. Then, the toner with external
additives was charged into a 25 ml glass bottle and placed at 50
and 80% humidity for 72 hours. Storage stability at a high
temperature was evaluated by observing the toner with external
additives with eyes. The results are summarized in Table 1 as
.smallcircle., .DELTA., .times., which indicates properties as
follows. [0104] .smallcircle.: No flocculation, thus no problem.
[0105] .DELTA.: weak flocculation but flocculated particles are
scattered when shaking, no substantial problem. [0106] .times.:
strong flocculation and not scattered, substantial problem.
[0107] Fixing Temperature Range: Resistance to Hot Offset
[0108] 100 g of toner, 2 g of silica (TG 810G; Cabot Co.) and 0.5 g
of silica (RX50, Degussa GmbH) were mixed to prepare a toner with
external additives. Using the toner with external additives,
unfixed solid images of 30 mm.times.40 mm were prepared by a
Samsung CLP-510 printer. Then, the fixing properties of the unfixed
images were evaluated while varying the temperature of a fixing
roller at a fixing tester in which the fixing temperature could be
controlled.
[0109] Charge Stability against Environment Changes
[0110] 0.2 g of each of the toner placed under three environmental
conditions (temperature/humidity) as follows for 16 hours and 2 g
of carriers were mixed at 150 rpm for 15 minutes. Then, a blow off
charge amount (Vertex Co.) was measured by a common method of
measuring charge amount of binary toner. [0111] 1) 10/10% 2) 25/55%
3) 32/80%
[0112] The results are shown in Table 1.
TABLE-US-00001 TABLE 1 Evaluation of toner performance Storage
stability Fixing Charge stability against at a high temperature
environment changes (uC/g) temperature range ( ) 10/10% 25/55%
32/80% Example 1 .smallcircle. 170-210 -23.5 -23.4 -22.4 Example 2
.smallcircle. 140-200 -24.8 -26.1 -25.5 Comparative 140-190 -24.5
-25.4 -17.4 Example 1 Comparative x 130-160 -24.1 -23.2 -16.9
Example 2
[0113] Referring to Table 1, storage stability at a high
temperature of the toner prepared in Examples 1 and 2 was better
than that of Comparative Examples 1 and 2. In addition, the fixing
temperature range of the toner prepared in Examples 1 and 2 was
140-210, and the fixing temperature range of the toner of
Comparative Examples 1 and 2 was 130-190. Accordingly, it can be
seen the fixing temperature range of the toner of Examples 1 and 2
is higher than that of Comparative Examples 1 and 2. Thus, the
occurrence of hot offset may be reduced in the toner of Examples 1
and 2 compared to the toner of Comparative Examples 1 and 2.
Furthermore, with regard to charge stability against environment
changes, while the charge amount of the toner of Examples 1 and 2
(-23.5.about.-24.8.fwdarw.-23.4.about.-26.1.fwdarw.-22.4.about.-25.5)
varies narrowly as the temperature and humidity increase, but the
charge amount of the toner of Comparative Examples 1 and 2 (31
24.1.about.-24.5.fwdarw.-23.2.about.-25.4.fwdarw.-16.9.about.-17.4)
varies widely. Thus, it can be seen that charge stability against
environment changes of the toner of Examples 1 and 2 is more
excellent than that of Comparative Examples 1 and 2.
[0114] As described above, since the toner according to the present
invention is formed of core particles including a polyester resin
and a shell including a styrene-acrylic resin, the toner can have
both advantages of the polyester resin having excellent anti-hot
offset properties and the styrene-acrylic resin having excellent
storage stability at a high temperature.
* * * * *